The round, brilliant white diamond is the only stone over 100 carats to have been given the highest grades in every criteria by the Gemological Institute of America.
A flawless diamond, the size of a large strawberry, is expected to fetch a world record price when it goes on sale at Sotheby's in London this month.
Weighing just over 102 carats, the round, brilliant white stone is smaller than a 163-carat oval diamond sold in Hong Kong in 2013, which currently holds the record price per carat.
But Sotheby's, which also handled that Hong Kong sale, expects the smaller stone's rarity and high quality will see it attract an even higher price.
"That (stone sold in Hong Kong) fetched $260,000 a carat, currently the world record for any colourless diamond. This one being a round brilliant cut - the asking price will be north of that," Patti Wong, chairman of Sotheby's Diamonds told Reuters.
The diamond is the only stone over 100 carats to have been given the highest grades in every criteria by the Gemological Institute of America, which judges a precious stone's quality, Sotheby's said.
It has not disclosed the asking price for the stone, which will be sold in a private sale.